Field
The embodiments disclosed herein generally relate to controlling erosion of plasma processing chamber components and etching uniformity of a substrate during plasma processing.
Description of the Background Art
Various semiconductor fabrication processes, such as plasma-assisted etching, physical vapor deposition, and chemical vapor deposition, among others, are often performed in plasma processing chambers in which a semiconductor work piece, such as a substrate, engages with a cover ring during processing. For example in a plasma processing chamber configured for etching a semiconductor substrate, the substrate is mounted on a substrate support pedestal within the processing chamber. The substrate support pedestal includes a metal electrode to which an RF bias may be applied. A plasma is formed from a mixture of process gases provided to the processing chamber. The pressure within the processing chamber is maintained by a pump which also removes by-products from the chamber. A power supply is coupled to the electrode inside the substrate support pedestal so as to produce on the electrode a negative bias voltage relative to the plasma. The bias voltage attracts the charged ions from the plasma to bombard the substrate so as to etch the substrate during processing. Because the electrode is negatively biased, the substrate support pedestal is often called the cathode.
The substrate is positioned inward of the cover ring while supported on the pedestal. Ions from the plasma gas formed in the chamber are biased by the cathode to target the substrate. During etching, the ions from the plasma tend to impact the substrate disposed on the substrate support at an angle normal to the plasma sheath. Over time, process equipment such as the cover ring, tend to erode from the ion bombardment. The erosion of the chamber components introduce contaminants into the chamber environment that substrate defects and shortens the mean time between maintenance as the chamber components must be serviced or replaced. Additionally, the erosion of chamber components may cause the plasma sheath to bend in a manner such that the trajectory of the plasma ions is no longer normal to the substrate. For example, erosion of the cover ring may cause plasma ions to angle toward the side or underside of the substrate, thus contributing to poor processing results, particularly near the edge of the substrate proximate the cover ring.
Therefore there is a need for an improved method for plasma processing of substrates in etch chambers.